Conventionally, an inter-vehicular distance controlling device is known (see Patent Document 1 for example). The inter-vehicular distance controlling device determines a curve radius of a lane on which a self vehicle is driving based on a steering angle detected by a steering sensor, recognizes a leading vehicle on the lane whose curve radius has determined, and controls an inter-vehicular distance between the self vehicle and the leading vehicle passing through the curve.
A travel path estimating device is also known (see Patent Document 2 for example). The travel path estimating device derives a conclusive curve radius by averaging a curve radius calculated on a steering angle or a yaw rate and a curve radius calculated on a motion of a stationary object located in front of a self vehicle and detected by a laser sensor. Then the travel path estimating device estimates a travel path of the self vehicle.
A curve radius estimating device which estimates a curve radius when a self vehicle is driving at a speed of more than 10 kilometers per hour (not at very slow speed) is also known (see Patent Document 3 for example). The curve radius estimating device corrects a curve radius calculated on a yaw rate with a steering angle and estimates a conclusive curve radius.
A vehicle controlling device which controls an inter-vehicular distance between a self vehicle and a leading vehicle is also known (see Patent Document 4 for example). The vehicle controlling device derives a curvature radius of a road on which a self vehicle is driving based on a yaw rate and a steering angle, recognizes a leading vehicle on the road having the derived curvature radius, and then controls the inter-vehicular distance between the self vehicle and the leading vehicle.    [Patent Document 1] Japanese Patent Publication No. H08-279099    [Patent Document 2] Japanese Patent Publication No. 2001-328451    [Patent Document 3] Japanese Patent Publication No. 2004-217178    [Patent Document 4] Japanese Patent Publication No. 2007-331608